Summary of Work: Toxoplasma gondii is an intracellular parasite with a wide host range. While infections of immunocompetent individuals are usually asymptomatic, congenital toxoplasmosis can lead to ocular and neurological abnormalities, while toxoplasmosis in immunocompromised individuals can cause serious illness or death. P30 (SAG 1) is a membrane-bound protein that is involved in attachment of the parasite to host cells. P30 is highly immunogenic and has been shown to offer significant protection against toxoplasmosis when used as an antigen. In an effort to determine which sequences of P30 are important in immune recognition, we performed peptide mapping utilizing overlapping peptides. Peptides, 15 amino acids in length and biotinylated at their amino termini, were synthesized. The peptides had an overlap of l0 amino acids and covered the entire 288 amino acids of the processed form of P30 and were probed by enzyme-linked immunosorbent assay (ELISA) with sera from either infected mice or mice immunized with P30. The results of these analyses indicated that there were three areas of the P30 sequence that were immunodominant. Each region was approximately 25 amino acids in length and was immunoreactive only with sera from exposed animals and not from naive mice. We are currently performing ELISA on shorter peptides in these areas to more precisely map the epitopes, and we will analyze the pattern obtained from mice immunized with purified P30. In addition, we are performing immunizations with the peptides identified as immunodominant to assess their use as vaccine candidates.